The present invention generally relates to image recording apparatuses and more particularly, to a transport mechanism for transporting photosensitive film sheets for use in an image recording apparatus of a laser beam type in which images are formed on the photosensitive film sheets by using laser beams.
Conventionally, there has been proposed for example, an image recording apparatus of this kind as shown in FIG. 1. The known apparatus includes a magazine 1 having photosensitive film sheets S stacked thereon, a suction means 2, a pair of nip rollers 3, an auxiliary scanning drum 4, a pair of nip rollers 5, a stopper 6 and a laser beam unit 7. The film sheets S are taken up from the magazine 1 one sheet at a time by the suction means 2 so as to fall down between the auxiliary scanning drum 4 and the nip rollers 5 through the nip rollers 3. Then, the stopper 6 is retracted from the auxiliary scanning drum 4 and, at the same time, the nip rollers 5 are brought into pressing contact with the auxiliary scanning drum 4 through the fallen film sheet S. Thus, when the film sheet S is being transported downwardly by a rotational force of the auxiliary scanning drum 4 which is rotated at all times, scanning of the laser beams is performed on the film sheet S by using laser beams irradiated from the laser beam unit 7 and thus, the images are formed on the film sheet S. Meanwhile, in sheet transport mechanisms for use in image recording apparatuses of this kind, in order to eliminate inaccurate scanning employing laser beams, it is generally necessary to eliminate unstable transport of the film sheet and transport the film sheet by positioning the film sheet accurately. However, in the known apparatus of FIG. 1, since it is so arranged that the film sheets S fall down by their own weight, it is difficult to accurately position the film sheets S due to variations in weight of the film sheets S or deflection of the film sheets S. Furthermore, in the known apparatus, the auxiliary scanning drum 4 is continuously rotated so as to prevent irregular rotation of the auxiliary scanning drum 4. However, since the nip rollers 5 are brought into and out of contact with the auxiliary scanning drum 4, torque of the drum 4 varies at the time of pressing contact of the nip rollers 5 with the drum 4, so that irregular rotation of the drum 4 takes place, thereby resulting in unstable transport of the film sheets S. Since even minute instability of transport of the film sheets S strongly affects reproducibility of the images in the case where an original having continuous tone, e.g., an X-ray film is reproduced, it is highly important to eliminate unstable transport of the film sheets S.